Show scroll bar on hover only

Signed-off-by: Philipp Hugenroth <philipph@spotify.com>

.changeset/late-pants-itch.md

@@ -0,0 +1,5 @@
+---
+'@backstage/core-components': patch
+---
+
+Show scroll bar of the sidebar wrapper only on hover

packages/core-components/src/layout/Sidebar/Items.tsx

@@ -299,12 +299,17 @@ export const SidebarScrollWrapper = styled('div')(({ theme }) => ({
   // Display at least one item in the container
   // Question: Can this be a config/theme variable - if so, which? :/
   minHeight: '48px',
-  '&::-webkit-scrollbar': {
+  overflowY: 'hidden',
+
+  '&:hover': {
+    overflowY: 'auto',
+  },
+  '&:hover::-webkit-scrollbar': {
     backgroundColor: theme.palette.background.default,
     width: '5px',
     borderRadius: '5px',
   },
-  '&::-webkit-scrollbar-thumb': {
+  '&:hover::-webkit-scrollbar-thumb': {
     backgroundColor: theme.palette.text.hint,
     borderRadius: '5px',
   },